While preparing to go to Vietnam in the early '70s, I received some of my best business training. In war, management of fear is constantly the issue. In actual combat, I noticed that fear created cowards out of some, and heroes out of others. Fear made some Marines smarter, while others became fools.

The same is true in business. Whenever I realize I did something stupid in business, it is either because I was too fearful, or not fearful enough. I was either acting too much like Pee-wee Herman or too much like Rambo.

One of the reasons many entrepreneurs stay small is because they act more like Pee-wee Herman. Looking back on my own career as an entrepreneur, I know I would have been far more successful if I were more like Rambo--if I had dreamed bigger dreams, taken on more impossible tasks and had a bigger vision of the possibilities. Too much of the time, I played it too safe.

My rich dad often said, "You cannot see the size of a person by looking at the person. You need to look at their reflection... what surrounds them."

Last November I was in New York City for a meeting with Donald Trump. Walking into his office building took my breath away. His reflection in his building is very big.

Later that day, I was on my way to the CNBC studios. Suddenly, off to my right, I noticed several tall, brand-new buildings with the name "Trump" on them. "Holy Cow!" was all I could say. I could only begin to guess how much work it had taken to clear so much land and erect so many buildings in Manhattan. Just dealing with the unions, city bureaucrats, environmentalists, the media and neighborhood committees would slay mere mortals. As the limo passed the rows of Trump Condominiums, I said to the driver, "Can you believe what Trump has done here?"

The driver smirked and said, "So what? You know he went broke once, so he's not that smart." I realized I was riding with Pee-wee, looking at the work of Rambo... and I was somewhere between the two of them.

As a Marine, I learned that fear, when it takes the form of self-doubt, kills more men than the enemy. The same is true in business--especially in entrepreneurship. Given the choice, I would rather be Rambo.

Robert Kiyosaki, author of the Rich Dadseries of books, is an investor, entrepreneur and educator whose perspectives have changed the way people think about money and investing.